Phototherapy and photochemotherapy for polymorphic light eruption desensitization: a five‐year case series review from a university teaching hospital

Dear Editor Polymorphic light eruption (PLE) is the most common immunological photodermatosis, with a prevalence of 18% in Europe (1). The pathogenesis of PLE appears to involve delayed cell-mediated hypersensitivity and aberrant Langerhans cell function (2, 3). Phototherapy, using narrowband UVB (UVB) or psoralen-ultraviolet A (PUVA) photochemotherapy, is widely used for prophylactic desensitization in PLE, with benefit experienced in 90% of patients (4, 5). The mechanism of desensitization is poorly understood but stratum corneum thickening, induction of immunomodulatory cytokines and changes in Langerhans cells and dermal mast cells may be implicated (6, 7). We describe five-year experience (2008–2013) of phototherapeutic desensitization for PLE. Patients with suspected photosensitivity (n = 1475) referred to the Scottish Photobiology Service, based at the Photobiology Unit, Ninewells Hospital and Medical School, Dundee, underwent investigations (including monochromator phototesting across the solar spectrum, UVA provocation testing, narrowband UVB minimal erythema dose (MED) testing and lupus serology). Of these 1475 patients, 370 (25%) were diagnosed with PLE. Of these 370 patients, phototherapeutic desensitization was offered to 109 and local Tayside case notes were available for review in 79 of these patients (76 UVB and 3 UVA1). Treatment numbers, occurrence of provoked PLE and response, as defined by use of repeat treatment courses in subsequent years, were recorded. The standard regimens used were as follows: Narrowband UVB phototherapy (or UVA1) three times a week (50% MED starting dose and 20% dose increments each treatment, unless erythema or PLE induced, in which case increments were reduced to 10% after erythema or PLE settled) for 15 treatments; PUVA (oral 8-methoxypsoralen 25 mg/m) twice-weekly for 15 treatments (70% minimal phototoxic dose (MPD) starting dose and 40%, reducing to 20% if erythema or PLE, dose increments at each treatment). If PLE was provoked, topical betamethasone valerate 0.1% ointment/cream was prescribed and treatment adjusted as described above. For the first course of desensitization, 46 patients (59%) received photo-exposed site treatment and 32 (41%) received whole body exposure (data missing for one patient). Following each treatment course, patients were encouraged to cautiously seek top-up sunlight exposure to maintain desensitization. Patients were followed up in autumn, and if deemed successful, the treatment was repeated yearly in spring. For patients who failed to obtain adequate desensitization after two consecutive years of UVB, PUVA was offered. Of the 79 patients with PLE who underwent desensitization, 67 were female; 12 male (median age 41 (range 12– 69) years). Fitzpatrick skin phototypes were as follows: I (n = 18), II (n = 42), III (n = 16) and IV (n = 3). Twentyeight patients had been investigated using monochromator phototesting, with normal responses in 27 (96%). The patient with abnormal responses showed borderline UVA